This is a blog detailing the creation/evolution/ID controversy and assorted palaeontological news. I will post news here with running commentary.

Wednesday, August 08, 2012

Two Hominin Species Running Around At 1.9 Mya

Meave Leakey and some colleagues1 have unearthed and described some new fossil hominins from Koobi Fora that seem to confirm that, yes, there were two very different critters running around 1.8 to 1.9 million years ago on the plains of eastern Africa. From the Turkana Basin Institute:

Found within a radius of just over 10 km from 1470’s location, the three new fossils are dated between 1.78 million and 1.95 million years old. The face KNM-ER 62000, discovered by field crew member Elgite Lokorimudang in 2008, is very similar to that of 1470, showing that the latter is not a single “odd one out” individual. Moreover, the face’s well-preserved upper jaw has almost all of its cheek teeth still in place, which for the first time makes it possible to infer the type of lower jaw that would have fitted 1470. A particularly good match can be found in the other two new fossils, the lower jaw KNM-ER 60000, found by Cyprian Nyete in 2009, and part of another lower jaw, KNM-ER 62003, found by Robert Moru in 2007. KNM-ER 60000 stands out as the most complete lower jaw of an early member of the genus Homo yet discovered.

The skull being referenced (heavily throughout the press release) is that of KNM-ER 1470, discovered by Richard Leakey in 1972 and dated to 1.9 million years ago. 1470 has a very flat face and is large, so much so that when it was discovered and compared to the Homo habilis material that Richard's dad, Louis Leakey and Napier and Tobias were pulling out of the ground, it was felt that it represented a new species, Homo rudolfensis.

Anyhow, these new fossils add a new level of what Bernard Wood2 calls “complexity.” For quite some time, 1470 existed in its own little world, with no fossil remains being similar to it in size or in shape. Questions began to rise about the veracity of its reconstruction and its provenance. These new fossils fit 1470 to a “T” and it now seems clear the 1470 does, in fact, represent a different form than that represented by skulls like ER 1813, which is small and gracile and gives support to the idea that there were two competing species of hominin on the landscape even before Homo erectus/ergaster arrived on the scene some two hundred thousand years later. Below, on the top is KNM-ER1813 and below it is KNM-ER 1470

As you can see, there is considerable difference in overall size and robusticity between the two and when the new material is compared to the mandible KNM-ER 1802, which is similar to 1813, there is a considerable mismatch. What remains to be seen is where Homo ergaster came from.

The distinction that is typically drawn is that the Chinese and South East Asian varieties of Homo erectus are quantitatively and qualitatively different from the ones in Africa, thus suggesting to some, like Bernard Wood, that the African variety needs a different taxonomic designation. I think it may be a distinction without a discernible difference but Wood and others don't see it that way.

As far as the appearance of Homo erectus/ergaster out of early Homo, there is even considerable disagreement about that. Several people argue that the big-brained early Homo sample could reasonably be folded into the Australopithecus taxon, thus putting things like A. sediba on equal footing for being the ancestor of H. erectus/ergaster. It is complicated.